U.S. Pat. No. 3,963,699 (Rizzi et al), issued Jun. 15, 1976, discloses the preparation of polyol polyesters (in particular sucrose polyesters), by a solvent-free, two-stage transesterification of the polyol (e.g., sucrose) with fatty acid lower alkyl esters (e.g., fatty acid methyl esters) by: (1) heating (preferably to from about 130.degree. to 145.degree. C. under a pressure of from about 0.5 mm to about 25 mm Hg.) a mixture of sucrose, methyl esters, alkali metal fatty acid soap and a basic catalyst to form a melt; and (2) adding to this melt excess methyl esters to provide the sucrose polyesters.
U.S. Pat. No. 4,517,360 (Volpenhein), issued May 14, 1985, discloses the preparation of polyol polyesters, in particular sucrose polyesters, by a solvent-free, two-stage trans-esterification of the polyol (e.g., sucrose) with fatty acid lower alkyl esters (e.g., fatty acid methyl esters) by: (1) heating (preferably to from about 130.degree. to 145.degree. C. under a pressure of from about 0.5 mm to about 25 mm Hg.) a mixture of sucrose, methyl esters, alkali metal fatty acid soap, and a potassium, sodium or barium carbonate catalyst to form a melt; and (2) adding to this melt excess methyl esters to provide the sucrose polyesters.
U.S. Pat. No. 4,518,772 (VolDenhein), issued May 21, 1985, discloses the preparation of polyol polyesters, in particular sucrose polyesters, by a solvent-free, two-stage transesterification of the polyol (e.g., sucrose) with fatty acid lower alkyl esters (e.g., fatty acid methyl esters) by: (1) heating (preferably to from about 130.degree. to 145.degree. C. under a pressure of from about 0.5 mm to about 25 mm Hg.) a mixture of sucrose, methyl esters, alkali metal fatty acid soap, and basic catalyst where the soap:sucrose molar ratio is from about 0.6:1 to about 1:1 to form a melt; and (2) adding to this melt excess methyl esters to provide the sucrose polyesters.
European patent application 256,585 (van der Plank et al), published Feb. 24, 1988, alleges that the catalysts used in the process of U.S. Pat. No. 3,963,699, and the way in which these catalysts are used, increases the risk of forming by-products, e.g., by ester condensation, leading to the formation of .beta.-ketoesters, e.g., by the reducing effect of sodium hydride, the recommended catalyst in the process of this U.S. patent. See page 2, lines 37-39. By-product formation is allegedly minimized by using a different process, e.g., forming an alkaline solution of sucrose which is then added to a mixture of soap and fatty acid methyl esters, followed by removal of the water and then heating to 110.degree.-140.degree. C. to form the sucrose polyesters.
European patent application 322,971 (Willemse), published Jul. 5, 1989, discloses a two-stage process for the transesterification of a polyol (e.g., sucrose) with fatty acid lower alkyl esters (e.g., fatty acid methyl esters) to provide polyol polyesters (e.g., sucrose polyesters). Pressure control is used during the first stage trans-esterification so that the sucrose is converted primarily to the corresponding monoesters and/or oligoesters, leading to higher yields of sucrose polyesters during the second stage transesterification. See page 2, right-hand column, lines 33-37. Pressure conditions used are from 60 to 180 millibars, preferably from 90 to 150 millibars. See page 3, left-hand column, lines 53-58. Pressure control during the first stage is also alleged to reduce foam formation. See page 2, right-hand column, lines 40-43. During the second stage, the pressure is reduced to less than 25 millibars, most preferably less than 5 millibars. See page 3, right-hand column, lines 15-23.
European patent application 349,059 (Willemse), published Jan. 3, 1990, discloses a process for making polyol polyesters (e.g., sucrose polyesters) in which a polyol and/or fatty acid oligoester thereof, is esterified by reaction with fatty acid lower alkyl esters (e.g., fatty acid methyl esters) in the presence of a transesterification catalyst and, optionally, an emulsifier. A stripping agent is used at least during the second stage of the transesterification to accelerate the removal of generated alcohol, e.g., methanol, to achieve high degrees (e.g., above 85%) of conversion to sucrose polyesters. See page 2, lines 46-54. Suitable stripping agents include inert gases, such as nitrogen, and volatile inert organic compounds, preferably hexane or short chain alkyl methyl esters. See page 3, lines 2-4 and 20-21.
European Datent application 323,670 (Meszaros et al). published Jul. 12, 1989, discloses a process for making polyol polyesters (e.g., sucrose polyesters) involving a two-stage transesterification of the polyol (e.g., sucrose) with a fatty acid lower alkyl ester (e.g., fatty acid methyl esters). The soap level is reduced after the reaction has reached a degree of conversion of from 15 to 60% to avoid undesired higher viscosities in the reaction mixture due to soap separation during the later stages of the reaction. See page 2, right-hand column, lines 18-23, and 27-43. This reduction in soap level can be carried out by a variety of methods, including filtration. See paragraph bridging pages 2 and 3.
U.S. Pat. No. 4,931,552 (Gibson et al), filed Jun. 14, 1989, issued Jun. 5, 1990, discloses the production of polyol polyesters (e.g. sucrose polyesters) having good color by reacting the polyol (e.g., sucrose) with lower alkyl esters of fatty acids (e.g., fatty acid methyl esters) having a "carbonyl content" or "carbonyl value" of less than about 200 ppm on a carbonyl group basis. See Column 2, lines 17-22. These "carbonyls" include unspecified ketones. See Column 2, lines 45-47. It is indicated that a special advantage of the lower carbonyl content of the lower alkyl esters of the fatty acid is that the level of esterification catalyst can be reduced to less than about 0.1, preferably to less than about 0.05, more preferably to less than about 0.01, molar equivalents of catalyst per mole of polyol. It is also stated that this low level of catalyst results in improved color as compared to conventional catalyst levels. See Column 7, lines 10-16.